Computer simulation of fluidity and microstructure of thin-sectioned cast iron

Abstract

Fluidity and microstructure of flake graphite cast iron with 3.3%C, 1.8%Si, 0.5%Mn, 0.05%P, 0.02%S were measured in thin sections of a step-shaped casting. Fe-Si inoculants were added to the hypoeutectic cast iron melt and plate-type fluidity tests with and without an overflow were undertaken. Structures within the fluidity specimens were classified into three zones from the tip backward: namely, ledeburite; mottled; and flake graphite structures. Structure is governed by the initial rate of cooling, which is dependent on the state of the mould at the time of contact with that part of the metal during flow. With overflow built in, fluidity length and the graphite structural zone were increased. This study aimed to investigate not only the fluid dynamics, but also the microstructure distribution within the range of flow of a hypoeutectic cast iron with flake graphite. Fluid flow and solidification microstructure were simulated using Stefan3D software. The heat diffusion and mould filling equations are solved by a finite difference method. The findings are expected to be developed into a technique to predict the fluidity and structure of production castings. A physical model for the evaluation of chill formation (grey/white structural transition) in iron castings was developed. This model is based on the concept of the existence of a critical cooling rate at which a grey to white transition occurs. Based on the physical model, the critical cooling rate for the grey/white structural transition was experimentally determined for a test casting of flake graphite cast iron. It was found that the effects of cooling conditions on the microstructure in cast iron can be satisfactorily simulated by computer.